1. Field of the Invention
This invention relates to a license plate tag for use in an electronic vehicular identification and communication system.
2. Description of the Prior Art
With the ever increasing volume of traffic on public highways, highway accidents have become a serious problem. There are presently, over 16 million highway accidents every year, resulting in approximately 5 million personal injuries and about 55,000 fatalities. There is thus a need for electronic safety measures such as traffic control, collision avoidance, automatic braking and wayside communication systems.
Further, with the increased volume of traffic, a need has arisen for remote means to identify or to control fast moving vehicles. Indeed, high speed chases of fugitives by police are notably hazardous, not only to the occupants of the offending vehicle and pursuing officers but also to innocent bystanders. Thus there is a need for means by which the pursuing police vehicle can remotely identify the offending vehicle. Moreover, there is an apparent need for an inexpensive means of communication between a wayside station and passing vehicles to inform such vehicles of hazardous conditions, detours, speed zones, etc.
Cooperative harmonic radars detecting and ranging systems for automotive vehicles, such as that disclosed in U.S. Pat. No. 3,781,879 to Staras et al., issued Dec. 25, 1973 are particularly advantageous for collision avoidance and automatic braking system in that they are immune to blinding by transmitted signals from other radar equipped vehicles and to clutter caused by extraneous targets. However such cooperative systems must be widely, if not totally, utilized to be effective. Acceptance of a cooperative system, it appears, is dependent, in part, on the cost to the user or subscriber.
A harmonic detection and identification system is disclosed in copending application to Richard Klensch, Ser. No. 428,721, filed Dec. 27, 1973 providing for a transmitter continuously transmitting a beam of electromagnetic energy in a predetermined direction so as to impinge upon an indentification tag suitably attached to a participating vehicle. The identification tag derives a harmonic signal from the impinging beam and radiates a beam of energy back to the transmitter at the harmonic frequency which is pulse modulated in accordance with the preset identification codes. The receiver receives the reflected beams and generates signals representative of the code modulation.